Segments (Summary of Assets by Segment and Reconciliation of Segment Assets to Total Assets) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Reconciliation of total segment assets to total assets
Assets	$ 9,041,245	$ 8,413,766
Operating Segments
Reconciliation of total segment assets to total assets
Assets	8,299,126	8,113,418
Operating Segments | Operating Assets
Reconciliation of total segment assets to total assets
Assets	3,911,853	3,476,718
Operating Segments | Master Planned Communities
Reconciliation of total segment assets to total assets
Assets	2,310,333	2,166,472
Operating Segments | Seaport District
Reconciliation of total segment assets to total assets
Assets	912,191	930,067
Operating Segments | Strategic Developments
Reconciliation of total segment assets to total assets
Assets	1,164,749	1,540,161
Corporate
Reconciliation of total segment assets to total assets
Assets	$ 742,119	$ 300,348